A group of mobsters seeking to break their boss out of the pen decide to do it by taking over the SS Tranquillity. In order to do so, they knock out the ships Captain MacTavish, and forge a note explaining his absence and the need for a replacement crew.

Meanwhile, Captain America and Bucky are en route for a voyage aboard the Tranquillity, a trip that Bucky moans will be boring. They soon find excitement when they stumble upon an escape attempt made by prisoners who have escaped from Seaside Penetentary. The heroes easily round up the escaped cons and turn them over to the arriving prison guards who tell them that one of the prisoners -- Harry Hawkins is still on the loose. Cap and Bucky tell the guards they'll keep an eye out for suspicious characters and continue on their way.

Aboard the ship, Captain America and Bucky notices the absence of MacTavish and the strange behaviour of the new crew. When Captain America hears some strange thumping, he tries to get the crew to help him investigate it, but they pass it off as nothing. Eventually, their voyage comes across a woman apparently stranded at sea. Bringing the girl aboard she introduces herself to Captain America as "Ms. Farney", however when the fake Captain brings her down to get some dry clothes they remark how she easily escaped Seaside. In reality, "Ms. Farney" is really Harriet "Harry" Hawkins.

While Hawkins and her gang are busy plotting to rob the passengers of the ship and leave them stranded, Captain America and Bucky hear the strange thumping again and go to investigate. In a storage closet they find that MacTavish is the source of the thumping, and upon untying him they learn of the crooks plot. Captain America and Bucky then quickly clash with Hawkins and her mob, easily defeating them and turning them over to the authorities.

Outside the War Department in Washington D.C., Colonel Carson is knocked out by Nazi spies and carried off to their secret hideout. There, the revived Carson is then taken to the spies leader, Herr Stoltz, who demands that he reveals military secrets. Carson refuses to do so, even under torture. However, after a lengthy torture session, Carson realizes that he cannot hold out forever and decides to commit suicide rather than betray his country. After scratching a message on his skin with a bed spring, Carson then hangs himself. When the Nazis return, they find his dead body. Stoltz orders them to dispose of it in the nearby river and they begin plotting another kidnapping.

Later, J. Edgar Hoover calls in the Human Torch and Toro to assist in the investigation of Carson's disappearance, which the FBI suspects is likely the work of Nazi spies. First they go to interview Carson's wife to see if she can recall seeing any suspicious individuals, however she does not recall anything strange, and the Torch promises that they'll find her husband.

The two heroes continue their search but come up with nothing until they happen by the waterfront as some children come across Carson's body in the water. The Torch and Toro recover the body and after informing Carson's widow and consoling her with the fact that her husband died in the service of his country, they go to examine the body. The Torch examines the corpse and finds a written message scratched on his body, which details sounds of travel that Carson heard as he was kept in the trunk of the Nazi's getaway car. With this information and determining the rate of which the body travelled down river the Torch and Toro pinpoint the location of the Nazis hideout.

However, their presence is seen by the Nazis and they lay out a trap for them. While the Torch and Toro round up the Nazis, their leader Stoltz makes a run for it. When the two heroes chase after him they are caught in a spring loaded trap that is fire proof. The Nazis then place the entrapment on the back of a flat bed truck intending to dump them in the river. However, the Torch and Toro bump around in the trap to make it fall off the back of the truck and break loose. Chasing the Nazis in their getaway vehicle, the Torch and Toro cause them to have a fatal crash, killing all aboard and avenging Carson's death.

In the underworld hideout of Rocky Scarpulla, Rocky meets with his gang and suggests that they "go straight" by posing as private detectives. To this end, they pay a visit to private detective Inspector Butts, and demand that he help them open their own agency. When Butts refuses, Rocky threatens to reveal that his adopted daughter is the daughter of mobster Killer Grogan, a man who Butts killed himself.

Overhearing part of this blackmail plot, Butts' adopted daughter Carol decides to help her father by getting in touch with the Destroyer. The Destroyer gets the call while he is working at his friend Jerry Crane's detective agency. Meeting with Carol he learns about Rocky Scarpulla's blackmail plot and goes to police headquarters to learn what he can about the crook.

Meanwhile, Rocky and his gang have fully taken over Butts Detective Agency and take on a job as security guards to transfer money from the First National Bank. To this end, they turn on the legitimate guards and attempt to steal the money, however they are opposed by the Destroyer, but they manage to escape. They next take a job to act as security at an exclusive party which will have many rich patrons with lots of valuable jewellery. As the gang leaves the Detectives office, the Destroyer breaks in and learns of their next job at the home of Mrs. Warburton.

The Destroyer goes to the party and overhear the Warburton's talk about how their daughter was kidnapped long ago by Killer Grogan and has never been seen since, and that the only thing they have to remember her by is part of a locket. As coincidence would have it Carol Butts ad her fiancée attend the party, and when Mrs. Warburton sees the other half of the locket warn around Carol's neck they realize that she is their long lost daughter. Suddenly, Rocky and his men storm the party and when the Destroyer tries to stop them he is knocked out and taken prisoner while the gang escapes. The gang then tries to eliminate the Destroyer by giving him a watery grave, but the hero breaks free from his bonds on their motorboat's engine and easily bests the gang and turns them over to the police. Freeing Inspector Butts he is reunited with his adopted daughter and they are all delighted to learn that Carol has finally been reunited with her biological parents.

A man reads in the newspaper that V.T.C. Pictures is going to begin reshooting the film "South Sea Paradise" and vows to prevent the production from completing.

Not far away on a Pacific Island, Director Spade begins preparations for the next days shooting and has one of his crew set up a camera set up in one of the massive palm trees. Witnessing this, the mystery man sneaks onto the set at night and cuts through the tree so that it topples the next morning. The next day, the Sub-Mariner is racing with fish when he happens upon the movie set and decides to take a look around. During the filming a stunt double is sent to climb up the palm tree, but it suddenly topples killing the actor. Namor officers his assistance and upon examination of the tree he finds evidence showing that it was deliberately cut and promises to find the person responsible.

Soon the next swimming scene involving the primary actor is to be shot next. When the actor dives into the water, he is followed by what appears to be a shark. However, it is the killer wearing a realistic shark-costume and he stabs the actor fatally. Witnessing this "shark attack", Namor arrives too late to save the actor, and the shark surprisingly manages to fight the hero off and disappear. Examining the dead actors body, the Sub-Mariner deduces that the man was not killed by a real shark, but really stabbed to death.

Searching the island, Namor finds footprints that lead to a mountain on the island. There he begins to feel weak from a lack of water and is easily captured by the killer, who locks him up in a room in his private cabin. Planning to kill the lead actress of the film, the killer reveals himself as John Rayburn, an actor who played in the original version of "South Pacific Paradise" until he was maimed in a shark attack. He then mocks the Sub-Mariner by leaving a bucket of water outside of the window of his prison knowing the hero is too weak to break free and will eventually die. However, Namor manages to free himself by tying the bed sheets to a pillow and using it as a sponge to bring the water to him and revitalize his strength.

Namor arrives at he scene before Rayburn can attack the starlet in his shark costume. Easily defeating Rayburn, the Sub-Mariner turns him over to the crew to hand over to the authorities. When the Director offers Namor a role in a film, he politely declines and returns to the ocean.

Notes

Although the narrative in the Captain America story identifies the characters as Steve Rogers and Bucky Barnes, as per the retcon from Captain America #215 these appearances are attributed to William Nasland and Fred Davis Jr. They are identified as such in this summary to avoid confusion.

This issue also features a brief 2-page educational story "Only the Beginning" which details various boats used throughout history.